WASHINGTON –– The World Trade Organization has rejected a Canadian request to require the United States to retroactively refund duties on softwood lumber if Canada successfully challenges the tariffs.

The 27 percent duties were imposed in May after a U.S. investigation found that Canadian provinces subsidize production of softwood lumber by charging low fees for harvesting trees on government land.

Ottawa pledged to fight the allegation through North American Free Trade Agreement and WTO panels – a fight that could take years.

The request for retroactive refunds was "part of Canada's broader strategy of contesting U.S. antidumping and countervailing duty orders on softwood lumber," according to a statement Thursday from the office of U.S. Trade Representative Robert Zoellick.

Last year the United States imported from Canada about $6 billion, or one-third, of its softwood lumber, which is used to frame and remodel houses.

Canadian producers from major lumber provinces such as British Columbia and Quebec say the U.S. tariffs are intended to protect American producers from Canadian competition.